1. Field of the Invention
This invention relates to an optical device and an apparatus using the optical device, the refractive index of which is varied by application of an external electric field.
2. Related Background Art
As prior art of the method for varying a refractive index by application of an external electric field, there is a method using nonlinear optical effect (see W. Primak et al., J. Electrochem Soc., 124(II), 1816-8(1977)). In other prior art of the method, ions are removed from glass by placing it at high temperatures and under high pressure so as to make refractive indexes of glasses as a property low by causing ion depletion in the glass (see D. E. Carlson et al., J. Amer. Ceram Soc., 57(7), 295-300 (1974) and D. E. Carlson et al., Am. Ceram Soc. Bull., 52(9), 705(1973)), dopants are added to glass substrates by using a method of electrically induced migration (see Chiba et al. a Journal of Electronic Communication Society, 85/7 vol. J68-C No. 7), and optical glasses having gradients of the refractive indexes are fabricated by ion exchange (see A. Feltz et al., DD0235864, WPI Acc No: 86-245898/38)).
But the method using nonlinear optical effect has the problems that high voltages KVs have to be applied to the optical device, which result in high-intensity electric fields occurring in the glass, and further, the high refractive index variations can not be obtained. On the other hand, it is possible to vary the refractive index as one property by the method of doping or depleting ions. But this refractive index variation is irreversible, and the refractive index cannot be reversibly controlled.